The present invention relates to fuel injection nozzles and more particularly relates to a fuel injection nozzle with a novel leak-off system.
One of the most common types of fuel injection nozzles employs a reciprocating needle which is spring-biased to its closed position and opened by fuel pressure. The major disadvantage with this type of fuel injection nozzle is that the fuel at the high pressure end of the valve will leak past the valve stem to a low pressure spring chamber. Unless some provision is made for draining the spring chamber, a hydraulic block could result. In order to prevent a hydraulic block, it has been common practice to employ a fuel leak-off conduit attached to the nozzle to return leakage fuel back to the reservoir or the intake of the pump. The drawbacks of this arrangement is that it complicates the installation and removal procedures by adding an additional conduit for each nozzle.
Many attempts have been made to obviate the need for leakoff conduits. One attempt has been to provide a draining passage for the leakage fuel directly to the intake manifold of the engine. This arrangement can result in an increased emission of smoke and hydrocarbons from the engine and can cause carbon deposits on the inlet valve.
In another attempt to eliminate the leak-off conduits, the fuel injection nozzle was provided with a large chamber for leakage fuel and reverse leakage during period of low pressure was relied upon to prevent hydraulic lock. This arrangement had the disadvantage of requiring a larger nozzle and the pressure in the chamber would build up to the point where it would effect opening of the valve.